Comments can be imported
from a PDF document. You can also import comments from a Form Data
Format (FDF) file or an XFDF file, which is an XML-based FDF file.
You cannot open and view FDF files or XFDF files on their own.
In the document that you want to receive comments, choose Comments > Import
Comments.
Choose All Files (*.*) from the menu. If you know the
file format of the comments you want to import, choose it.
Double-click the name of the document with the comments.
The comment positioning matches that of the file
from which they were imported. If comments appear out of place,
the source and recipient PDF documents are likely different. For
example, if you import comments from a ten-page document to a two-page
document, only comments from the first two pages appear.